Recent experiments in the presynaptic terminal of the squid giant synapse indicate that the relation between inward calcium current and the synaptic release process is amenable to detailed examination using voltage clamp techniques. Further study of the voltage dependent calcium conductance change must be done to obtain information regarding the relationship between membrane potential and calcium current at varying extracellular calcium concentrations. A similar set of experiments will be done to determine the temperature dependence of this process (Q10) as well as on the time course of calcium permeability onset. The experiments would also allow study of the nature of synaptic delay and its relation to calcium concentration and temperature. In a third set of experiments the nature of synaptic facilitation will be studied. The possibility as to whether facilitation is due to increased calcium permeability to a second depolarization or to a momentary increase of intracellular calcium will be determined.